Method of manufacturing silicon single crystal, silicon single crystal and silicon wafer

ABSTRACT

The present invention is a method of manufacturing a silicon single crystal by Czochralski method without performing Dash Necking method, wherein a temperature variation at a surface of a silicon melt is kept at ±5° C. or less at least for a period from a point of bringing the tip end of a seed crystal into contact with the silicon melt to a point of shifting to pull the single crystal. Thereby, in a method of growing a silicon single crystal by Czochralski method without using Dash Necking method, a success ratio of growing a single crystal free from dislocation can be increased, at the same time a heavy silicon single crystal having a large diameter in which a diameter of a constant diameter portion is over 200 mm can be grown even in the case of growing a silicon single crystal having a crystal orientation of &lt;110&gt;.

TECHNICAL FIELD

The present invention relates to a method of manufacturing a siliconsingle crystal using Czochralski method (hereinafter, occasionallyreferred to as “CZ method”), more particularly, a method ofmanufacturing a silicon single crystal grown by Chochralski method byuse of a seed crystal having a tip end with a sharp-pointed shape or atruncation thereof without using Dash Necking method, and a siliconsingle crystal and a silicon wafer manufactured thereby.

BACKGROUND ART

A silicon wafer, which is obtained by processing a silicon singlecrystal grown by mainly CZ method into wafers, is used as a wafer for asubstrate material on which a semiconductor device is formed. In growthof a silicon single crystal using CZ method, generally a seed crystalhaving a shape shown in FIG. 2(A) or 2(B) is gently brought into contactwith a silicon melt heated to 1420° C. of a melting point or more, andthen the seed crystal is gradually pulled upward from the melt when atemperature of the seed crystal becomes steady. Thereby, a siliconsingle crystal is grown below the seed crystal. At this time, becauseinnumerable slip dislocations are generated in the seed crystal as aresult of thermal shock arising when the seed crystal is brought intocontact with the silicon melt of high temperature, a necking portionwhere a diameter of the crystal grown following the seed crystal is oncegradually lessened to about 3–5 mm is formed as shown in FIG. 4 in orderto eliminate the slip dislocations. When the slip dislocations can havebeen eliminated from the grown crystal, a diameter of the crystal isgently enlarged to a desired diameter (formation of an enlargingdiameter portion), and then an approximately cylindrical silicon singlecrystal having a diameter required in a constant diameter portionthereof is pulled.

A method of eliminating slip dislocations generated when a seed crystalcomes into contact with a silicon melt by lessening a diameter of thecrystal to about 3–5 mm is called as Dash Necking method, which is amanufacturing method widely utilized when growing a silicon singlecrystal by CZ method.

On the other hand, in recent manufacture of a silicon single crystal, atype of production in which a constant diameter portion of the singlecrystal is lengthened as much as possible is adopted in order to improvea productivity of a silicon single crystal itself and a silicon waferhaving a large diameter is required with the aim of obtaining a largesemiconductor device and improving a yield. Therefore, a single crystalto be pulled is becoming larger in diameter and heavier in weight.

In cases that such a heavy silicon single crystal having a largediameter is grown, there naturally occurs a limit to the productionusing Dash Necking method in which a diameter of a neck portion islessened to 5 mm or less, otherwise slip dislocations can not beeliminated.

Therefore, recently a method of growing a silicon single crystal freefrom dislocation without using Dash Necking method is also beingstudied. For example, in Japanese Patent Application Laid-Open (kokai)No. 10-203898, a technique in which a silicon single crystal is grownwithout forming a neck portion by using a seed crystal having a tip endwith a sharp-pointed shape or a truncation thereof is disclosed.

If the technique disclosed in the Japanese Patent Application Laid-Open(kokai) No. 10-203898 is used, a silicon single crystal free fromdislocation can be grown without lessening a diameter of the crystal tobe grown at the tip end of the seed crystal to 5 mm or less. Therefore,it has an advantage in growing a crystal having a large diameter or aheavy crystal.

However, in the technique of manufacturing a silicon single crystaldescribed in the aforementioned Japanese Patent Application Laid-Open(kokai) No. 10-203898, there is a problem of how to adjust operationconditions so as not to generate slip dislocations when the seed crystalis brought into contact with a silicon melt. Even if a seed crystalhaving a tip end with a sharp-pointed shape or a truncation thereof isused, in the case where a difference of temperatures between the seedcrystal and the silicon melt when the seed crystal comes into contactwith the silicon melt is larger than required, innumerable slipdislocations are introduced into the seed crystal and it is impossibleto eliminate the slip dislocations without necking. Moreover, manypoints to be studied in terms of operation has remained, for example,slip dislocations are introduced into the seed crystal if thetemperature of a silicon melt largely changes even while the tip end ofthe seed crystal is dipped into the silicon melt to the desired diameterand so on.

As for the silicon wafer, a silicon wafer having a plane orientation of(100) or (111) in a main surface on which a semiconductor device is tobe formed has been mainly utilized in view of physical characteristicsand advantages in the processes of growing a crystal and fabricating asemiconductor device. However, since transport of carriers when forminga semiconductor device considerably depends on a crystal orientation, inrecent years, with the aim of enhancing the working speed of thesemiconductor device, a silicon wafer having a plane orientation of(110) in which high switching speed is expected starts to attractattention (Nikkei Microdevices, the February 2001, No. 188, Nikkei BPInc., published on Feb. 1, 2001).

In order to obtain the silicon wafer having a plane orientation of(110), it is possible to utilize a method in which a silicon singlecrystal having a crystal orientation of <100> or <111> is processed sothat a (110) plane may be a main surface of a wafer, or a method inwhich a silicon single crystal having a crystal orientation of <110> isgrown from the first and processed into a silicon wafer. However, theformer method in which a silicon wafer having a plane orientation of(110) in a main surface thereof is manufactured from a single crystalhaving a crystal orientation of <100> or <111> requires oblique cuttingof the cylindrical crystal so that the main surface may be a (110)plane. Therefore, it is not an efficient method for industrial massproduction of silicon wafers because, in order to obtain anapproximately circular silicon wafer to be a substrate for a standardsemiconductor device, stock removal for making its shape becomes greatloss and time for processing is long.

To the contrary, in the method in which a single crystal having acrystal orientation of <110> is grown from the first and a silicon waferwith a main surface of a (110) plane is manufactured therefrom, if thesilicon single crystal is sliced perpendicularly to the direction of thepulling axis as in the case of manufacturing silicon wafers having otherplane orientations, and mirror-polishing is performed, a silicon waferhaving a main surface of a (110) plane can be obtained. According tothis method, since processing after pulling a single crystal can beperformed as in the case of a wafer having a plane orientation of (100)or (111), grinding loss generated when making a shape of a wafer andprocessing time for making the shape can be minimized. Thereforeeffective wafer processing without loss can be performed.

However, this method has a problem in growing a silicon single crystalhaving a crystal orientation of <110>.

Namely, in the case of a crystal having a crystal orientation of <100>or <111>, since slip dislocations caused in a seed crystal by thermalshock are introduced at an angle of about 50–70° to a crystal growthinterface, the slip dislocations can be taken out (eliminated) from acrystal to be grown by decreasing a diameter of the crystal to about 3–5mm. However, in the case of a crystal having a crystal orientation of<110>, because slip dislocations are introduced in the directionapproximately perpendicular to a crystal growth interface, it isdifficult to eliminate the slip dislocations easily from the crystal tobe grown. Consequently, there is a need to grow a silicon single crystalusing a method in which a diameter of a neck portion is extremelylessened to less than 2 mm as described in Japanese Patent ApplicationLaid-open (kokai) No. 9-165298 etc., or a special method in which, forexample, slip dislocations are taken out by forming multi-step concavityand convexity at a neck portion through repeated operation of lesseninga diameter of a neck portion to about 3–5 mm and then enlarging thediameter.

Particularly in the case of growing a silicon single crystal having acrystal orientation of <100> or <111>, if a few slip dislocations aregenerated at a tip end of a seed crystal by thermal shock, the slipdislocations can be eliminated by virtue of using a seed crystal havinga tip end with a sharp-pointed shape or a truncation thereof while theseed crystal is dipped to the desired diameter. However, in the case ofa crystal having a crystal orientation of <110>, because slipdislocations are introduced in the direction approximately perpendicularto a melting surface of a seed crystal as described above, it isextremely difficult to eliminate even a few slip dislocations onceintroduced into the seed crystal.

Thus, in order to grow a silicon single crystal having a crystalorientation of <110> by use of a seed crystal having a tip end with asharp-pointed shape or a truncation thereof without using Dash Neckingmethod, there is a need to form further adequate operation conditionsthan the case of growing a silicon single crystal having a crystalorientation of <100> or <111>.

Moreover, also in the case of growing a silicon single crystal having acrystal orientation of <110>, for production of a heavy silicon singlecrystal with a large diameter, if a neck portion is formed by DashNecking method to eliminate slip dislocations and further the minimumdiameter of the neck portion is lessened to about 2–3 mm to ensureelimination of dislocations, it is hardly possible to pull a siliconsingle crystal with a large diameter of 200 mm or more and weight of 100kg or more. In order to support such a heavy silicon single crystal witha large diameter and pull it, there is a need that a diameter of acrystal formed at a tip end of a seed crystal is kept to 5 mm or moreeven at a portion with minimum diameter.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a method ofmanufacturing a silicon single crystal, in which a success ratio ofgrowing a single crystal free from dislocation is increased when growingthe silicon single crystal using a seed crystal having a tip end with asharp-pointed shape or a truncation thereof by CZ method without Dashnecking method, and at the same time, even in the case of growth of asilicon single crystal having a crystal orientation of <110>, a siliconsingle crystal with a large diameter can be grown by setting a minimumdiameter of the crystal formed at a tip end of the seed crystal to 5 mmor more so that a diameter of a constant diameter portion of the singlecrystal may be 200 mm or more, a silicon single crystal, and a siliconwafer having a large diameter of 200 mm or more with a plane orientationof (110).

In order to accomplish the above object, a method of manufacturing asilicon single crystal of the present invention is a method ofmanufacturing a silicon single crystal by Czochralski method withoutperforming Dash Necking method, comprising the steps of: providing aseed crystal having a tip end with a sharp-pointed shape or a truncationthereof in which an angle of the tip end is 28° or less; keeping the tipend of the seed crystal just above a silicon melt to heat it beforebringing the tip end of the seed crystal into contact with the siliconmelt; subsequently bringing the tip end of the seed crystal into contactwith the silicon melt and immersing the seed crystal into the siliconmelt to a desired diameter; and then shifting to pull the singlecrystal, wherein a temperature variation at a surface of the siliconmelt is kept at ±5° C. or less at least for a period from a point ofbringing the tip end of the seed crystal into contact with the siliconmelt to a point of shifting to pull the single crystal.

Since Dash Necking is not performed, a diameter of the crystal formed atthe tip end of the seed crystal can be kept to 5 mm or more. Therefore,a silicon single crystal having a large diameter of 200 mm or more andweight of 100 kg or more can be pulled.

Particularly in the case of growing a silicon single crystal free fromdislocation using a seed crystal having a tip end with a sharp-pointedshape or a truncation thereof without performing Dash Necking (in whicha diameter of a crystal formed at a tip end of a seed crystal is oncelessened to about 3–5 mm to eliminate slip dislocations), it isdesirable that the crystal is grown by use of a seed crystal having atip end with a sharp-pointed shape or a truncation thereof in which anangle of the tip end is 28° or less. The success ratio of growing asingle crystal free from dislocation can be increased by using the seedcrystal of which an angle of the tip end is 28° or less.

If the angle of the tip end is 28° or less, it is easy to moderatethermal shock generated when the seed crystal is brought into contactwith the silicon melt. Further, even in the case of generating a fewslip dislocations, it is easy to let slip dislocations out of the seedcrystal if the angle of the tip end is 28° or less. However, in the caseof the angle of the tip end of more than 28°, heat capacity at the tipend portion of the seed crystal increases, and temperature differencewhen bringing the tip end into contact with the silicon melt generatesthermal shock. Thereby slip dislocations are introduced into thecrystal. Moreover, since a diameter of the tip end of the seed crystalafter dipping into the silicon melt becomes large by itself, it becomesdifficult to let the introduced slip dislocations out of the crystal.

For these reasons, in the manufacturing method of the present invention,the seed crystal having a tip end with a sharp-pointed shape or atruncation thereof in which an angle of the tip end is 28° or less isutilized to suppress thermal shock when bringing the seed crystal intocontact with the silicon melt.

It is necessary to heat the seed crystal just above the silicon melt soas to be approximately the same temperature as a surface of the siliconmelt before bringing the above-mentioned seed crystal into contact withthe silicon melt.

By heating the seed crystal before bringing it into contact with thesilicon melt to set a temperature of the tip end of the seed crystalsufficiently close to a temperature of the silicon melt, the temperaturedifference between the tip end of the seed crystal dipped into thesilicon melt and the silicon melt is made little, and thereby generationof thermal shock can be suppressed. At this time, heating of the seedcrystal just above the silicon melt is performed preferably for about5–60 min, optimally for about 20–30 min.

If the tip end of the seed crystal is heated for a range of 5–60 min,the temperature of the tip end of the seed crystal can be setefficiently close to the temperature of the silicon melt surface, andfurther productivity of the silicon single crystal is not decreased bythe heating. More optimally, an interval between the silicon melt andthe tip end of the seed crystal is kept in a range of about 1–5 mm andthe seed crystal is heated for 20–30 min, and then it is dipped into thesilicon melt. Thereby, the thermal shock when bringing the seed crystalinto contact with the silicon melt can be suppressed as small aspossible.

Moreover, there is a need to perform dipping while a temperaturevariation at a surface of the silicon melt near the seed crystal is keptat ±5° C. or less for a period from bringing the tip end of the seedcrystal into contact with the silicon melt and immersing it into thesilicon melt up to a desired diameter to shifting to pulling the singlecrystal.

Since the silicon melt is kept as a melt by heating with a heaterdisposed around it, the silicon melt always generates thermal convectionand temperature thereof constantly varies a little. When the temperaturevariation by the thermal convection is too large, even if the seedcrystal is heated in conformity to the temperature of the silicon meltand then is brought into contact with the melt, thermal shock isgenerated at the tip end of the seed crystal. Thereby slip dislocationsare introduced into the seed crystal. In addition, when the tip end ofthe seed crystal is dipped into the silicon melt, if a temperature ofthe silicon melt near the seed crystal changes large during dipping ofthe tip end, thermal strain is generated in the seed crystal throughtemperature difference between the seed crystal and the melt. Therebyslip dislocations are introduced into the seed crystal, and it becomesdifficult to grow a single crystal free from dislocation thereafter.

In order to suppress such introduction of slip dislocations as much aspossible, there is a need to pull the single crystal while thetemperature variation at the surface of the silicon melt near the tipend of the seed crystal is kept at ±5° C. or less from a temperaturewhen bringing the seed crystal into contact for a period from a point ofbringing the tip end of the seed crystal having a sharp-pointed shape ora truncation thereof into contact with the silicon melt to a point ofimmersing the tip end into the silicon melt to a desired diameter andshifting to pulling. If the temperature variation of the silicon melt isover ±5° C., it becomes easier to introduce slip dislocations into theseed crystal at the time of contact with the melt or dipping, andtherefore the success ratio of pulling a silicon single crystal freefrom dislocation is decreased.

In particular, in a silicon single crystal having a crystal orientationof <110>, from which it is difficult to eliminate slip dislocations onceintroduced thereinto, if the temperature variation of the silicon meltis over ±5° C., possibility of growing a silicon single crystal freefrom dislocation extremely decreases. In order to at least pull asilicon single crystal having a crystal orientation of <110> by use of aseed crystal having a tip end with a sharp-pointed shape or a truncationthereof without performing Dash Necking, there is a need to dip the seedcrystal to the desired diameter while a temperature variation of thesilicon melt near a portion where the tip end of the seed crystal isdipped is kept at ±5° C. or less as compared to the temperature of themelt when bringing the seed crystal into contact with the melt.

More preferably, the temperature variation of the silicon melt issuppressed to ±3° C. or less. If the pulling is performed while thetemperature variation of the melt near the dipped portion of the seedcrystal is further decreased so that it is kept at ±3° C. or less ascompared to the temperature of the melt when bringing the seed crystalinto contact with the melt, slip dislocation due to the temperaturevariation of the silicon melt is hardly generated even in the case of asingle crystal having a crystal orientation of <110>. Therefore, asilicon single crystal having no dislocation and the desired diametercan be almost surely pulled.

It is preferable that the seed crystal is brought into contact with thesilicon melt and immersed therein with setting a temperature of thesilicon melt when bringing the tip end of the seed crystal into contactwith the silicon melt to 10–20° C. higher than a temperature appropriatefor bringing the seed crystal into contact with the silicon melt in amethod of manufacturing a silicon single crystal using Dash Neckingmethod, and the single crystal is pulled with setting a pulling rate to0.5 mm/min or less at least when forming a decreasing diameter portionfor a period from a point immediately after stopping lowering of theseed crystal and shifting to pulling to a point of starting enlargementof a diameter of the crystal formed below the seed crystal.

In a method of manufacturing a silicon single crystal using Dash Neckingmethod, in the case that the temperature of the silicon melt is lowerthan a temperature appropriate to contact of the seed crystal with thesilicon melt, or in the case that even though higher, the difference isless than 10° C., when the seed crystal is dipped into the silicon melt,the dipped portion can not be smoothly melt into the silicon melt. As aresult, there is a possibility of bringing about anomalous crystalgrowth such as occurrence of solidification.

To the contrary, if the temperature of the silicon melt is over 20° C.higher than a temperature appropriate to contact of the seed crystalwith the silicon melt in a method of manufacturing a silicon singlecrystal using Dash Necking method, the tip end is melted before the seedcrystal is brought into contact with the silicon melt. As a result,there is a possibility to be unable to successfully bring the seedcrystal into contact with the silicon melt.

Considering the above, the seed crystal should be brought into contactwith the silicon melt and immersed therein while the temperature of thesilicon melt when dipping the seed crystal is kept in a range of 10–20°C. higher than the temperature appropriate to contact of the seedcrystal with the silicon melt in a method of manufacturing a siliconsingle crystal using Dash Necking method.

Then, in formation of a decreasing diameter portion for a period from apoint immediately after finishing immersing of the tip end of the seedcrystal into the silicon melt to the desired diameter and stoppinglowering of the seed crystal to shift to pulling to a point of startingenlargement of a diameter of the crystal formed below the seed crystal,it is desirable that the silicon single crystal is grown while keeping apulling rate at 0.5 mm/min or less.

At a point immediately after finishing immersing the tip end of the seedcrystal to the desired diameter and shifting to pulling, a diameter of acrystal formed below the seed crystal once becomes a little smaller thana diameter at a point of finishing immersing of the seed crystal, andthen growth of the crystal is performed (formation of a decreasingdiameter portion). At this time, if pulling is performed at a higherrate than required, the diameter of the crystal grown below the seedcrystal becomes much smaller than a desired diameter, and as the casemay be, disadvantage such as separation of the crystal from the siliconmelt occurs.

In order to solve such problems, when forming a decreasing diameterportion for a period from a point after stopping immersing of a seedcrystal and shifting to pulling to a point of starting enlargement of adiameter of a crystal formed below the seed crystal, it is adequate toperform growth of a crystal while keeping a pulling rate at 0.5 mm/minor less.

In order to make it easy to set the above-mentioned conditions ofcontacting with the melt and dipping of the seed crystal, it ispreferable that the silicon single crystal is grown while a horizontalmagnetic field with the magnetic field intensity of 1000 G or more at acenter thereof is applied to the silicon melt at least for a period froma point of bringing the tip end of the seed crystal into contact withthe silicon melt to a point of completing formation of the decreasingdiameter portion formed below the seed crystal and starting enlargementof the diameter of the crystal.

In the present invention, it is important to perform growth while thetemperature variation of the silicon melt near the portion where the tipend of the seed crystal is dipped is kept at ±5° C. or less as comparedto the temperature of the melt when bringing the seed crystal intocontact with the melt. In order to suppress such a temperature variationof the silicon melt contained in a crucible, it is necessary to suppressthermal convection of the silicon melt generated by heating with heaterdisposed around the crucible as little as possible. In order toefficiently suppress the thermal convection, Magnetic field applied CZmethod (hereinafter, referred to as MCZ method) in which a singlecrystal is grown with applying a magnetic field to a silicon melt issuitable for use. Particularly, in order to stabilize a temperature ofthe silicon melt near the seed crystal when bringing the seed crystalinto contact with the melt and dipping it thereinto, it is desirablethat the seed crystal is brought into contact with the melt and dippedthereinto while applying to the silicon melt a horizontal magnetic fieldwhich has a great effect on decreasing temperature gradient of thesilicon melt in the crucible. Such methods of growing a silicon singlecrystal include Horizontal magnetic field applied CZ method(hereinafter, referred to as HMCZ method).

If the tip end of the seed crystal is brought into contact with thesilicon melt and dipped into the melt to the desired diameter whileapplying to the silicon melt a magnetic field with intensity of 1000 G(Gauss) or more by means of this HMCZ method, it becomes easy tosuppress the temperature variation of the silicon melt near the dippedportion to ±5° C. or less in the meantime. However, without limiting tosuch a controlling method, even in the case of a magnetic field withintensity of less than 1000 G or the case of no magnetic field applied,thermal convection can be suppressed by other controlling methods, forexample, by heating a surface of the silicon melt through lamp heatingto decrease the temperature gradient in the vertical direction insidethe silicon melt. Thermal convection of the silicon melt can be alsosuppressed by setting the amount of the silicon melt less and making adepth of the melt shallow. Further, if growth is performed whilesuppressing the temperature variation of the silicon melt at a portionwhere dipping the seed crystal to ±5° C. or less by combination withapplication of a magnetic field or the like, similar effect can beobtained.

In the case of appropriately suppressing the temperature variation ofthe silicon melt through application of a magnetic field to the siliconmelt, it is preferable that a horizontal magnetic field of whichintensity at the center is 1000 G or more is applied to the siliconmelt, and a seed crystal having a tip end with a sharp-pointed shape ora truncation thereof is brought into contact with the melt and dippedthereinto.

As for the maximum intensity of the magnetic field applied to thesilicon melt, taking a configuration of an apparatus or application of amagnetic field in a practical range into consideration, the upper limitof the magnetic field intensity at the center is at most about9000–10000 G as it stands in the case of HMCZ method.

A method of pulling a silicon single crystal while applying a horizontalmagnetic field of 1000 G or more to a silicon melt using the HMCZ methodis also effective in the case of growing a large silicon single crystalhaving a diameter over 200 mm. In the case of growing a single crystalwith a large diameter, taking productivity or yield into consideration,generally a single crystal is grown by using a large crucible forcontaining a silicon melt and charging a large amount of raw materialover 100 kg into the crucible at a time.

When the amount of the raw material contained in the crucible, i.e., thesilicon melt, is large, temperature difference between a peripheralportion of the silicon melt near heater and a portion near the center ofthe melt becomes large. Thereby, it becomes difficult to stabilize thetemperature of the melt near a dipped portion of a seed crystal sincethermal convection becomes active. At this time, if a desired magneticfield of 1000 G or more is applied to the silicon melt, the temperatureof the melt near the dipped portion of the seed crystal can bestabilized since thermal convection in the crucible can be suppressed.

Intensity of the horizontal magnetic field applied to the silicon meltmay be appropriately selected in accordance with a diameter and qualityconditions of a single crystal to be grown in addition to stability of atemperature of the silicon melt.

If such a method of manufacturing a silicon single crystal is utilized,the temperature of the melt when bringing the seed crystal having a tipend with sharp-pointed shape or a truncation thereof into contact withthe silicon melt and dipping it thereinto is stabilized. Therefore, theseed crystal can be dipped to the desired diameter so as to decreasegeneration of slip dislocations due to thermal shock as much as possibleor to generate no slip dislocation.

Thereby, the success ratio of pulling a silicon single crystal having adesired constant diameter portion free from dislocation can beincreased, and at the same time a silicon single crystal having acrystal orientation of <110> can be pulled by use of a seed crystalhaving a crystal orientation of <110>, which has been considereddifficult in growth of a silicon single crystal using CZ method due torestriction by Dash Necking method. Also, it becomes possible to pull asilicon single crystal grown by Czochralski method which has a crystalorientation of <110> and a constant diameter portion with a diameter of200 mm or more, or such a silicon single crystal wherein total weight ofthe crystal pulled from a silicon melt is 100 kg or more, further over300 kg.

If the silicon single crystal having a crystal orientation of <110>grown by the aforementioned manufacturing method is subjected tocylindrical grinding, slicing and mirror-polishing using the samemanufacturing process as in the case of a crystal having a crystalorientation of <100> or <111>, a silicon wafer having a planeorientation of (110) in a main surface thereof, which is a main rawmaterial when manufacturing a semiconductor device, can be industriallymanufactured with high efficiency.

In particular, since it becomes possible to obtain a silicon singlecrystal having a diameter of more than 200 mm in a constant diameterportion and a crystal orientation of <110>, which has been considereddifficult to be grown in a conventional method, a silicon wafer having amain diameter of 200 mm or more and a plane orientation of (110) in amain surface can be easily produced. Here the main diameter of thesilicon wafer refers to a diameter of a main surface of the wafer notincluding an orientation flat or an orientation notch.

If the silicon wafer has a plane orientation of (110) and a diameter of200 mm or more, a semiconductor device having advanced function can bemanufactured with good yield and in large quantities.

In growth of a silicon single crystal having a crystal axis orientationof <110>, since slip dislocations due to thermal shock when a seedcrystal comes into contact with a silicon melt are introduced in thedirection approximately perpendicular to a crystal growth interface, itis difficult to eliminate the slip dislocations in a method using DashNecking method, and therefore, mass production has been difficult.Furthermore, in growth of a silicon single crystal having a crystalorientation of <110> using Dash Necking method, since a diameter of aneck portion needs to be lessened to 2 mm or less in order to eliminateslip dislocations, it has been considered difficult to efficientlymanufacture a heavy crystal with a large diameter of 200 mm or more, or300 mm or more.

However, in accordance with the manufacturing method of the presentinvention, it becomes possible to safely and efficiently produce even asilicon single crystal with a crystal orientation of <110> having alarge diameter of more than 200 mm, or a silicon single crystal with acrystal orientation of <110> of which the constant diameter portion waspulled as long as possible and which has a weight of 100 kg or more.

At the same time, in growth of a silicon single crystal having a crystalorientation other than <110> by adopting a Dislocation-free seedingmethod in which a silicon single crystal is grown without using DashNecking method, an effect of increasing the success ratio of pulling asingle crystal free from dislocation can be obtained.

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1 is a schematic view of an apparatus for manufacturing a singlecrystal by CZ method, in which a magnetic field applied apparatus isinstalled, for conducting a method of manufacturing a silicon singlecrystal according to the present invention.

FIG. 2 is a drawing showing seed crystals used in Dash Necking method,and seed crystals, each of which has a tip end with a sharp-pointedshape or a truncation thereof used in the manufacturing method of thepresent invention.

FIG. 3 is a photograph showing a portion of a silicon single crystalhaving a crystal orientation of <110> and a diameter of about 200 mmgrown by means of the manufacturing method of the present invention.

FIG. 4 is a drawing for illustrating removal of slip dislocations byDash Necking method.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter embodiments of the present invention will be explained withreference to appended drawings. Drawings shown in FIGS. 2(C), 2(D), 2(E)and 2(F) are schematic views showing each seed crystal having a tip endwith a sharp-pointed shape or a truncation thereof used in growth ofsilicon single crystals according to the present invention.

In FIGS. 2(C) and 2(D), FIG. 2(C) shows a seed crystal 1 c having acylindrical straight body 3 c with a conical tip end 4 c, and FIG. 2(D)shows a seed crystal 1 d having a prismatic straight body 3 d with apyramidal tip end 4 d.

Each of FIGS. 2(E) and 2(F) shows a tip end of a seed crystal having ashape in which the tip end 4 c of the seed crystal shown in FIG. 2(C) istruncated. FIG. 2(E) shows a tip end 4 e in which the tip end 4 c of theseed crystal 1 c is horizontally truncated, and FIG. 2(F) shows a tipend 4 f in which the tip end 4 c is obliquely truncated. As to seedcrystals having shapes of truncated tip end, if the areas of the bottomparts of the tip ends 4 e and 4 f shown in FIGS. 2(E) and 2(F)respectively are too large, thermal shock is likely to occur when theseed crystals come into contact with a melt. Therefore it is preferablethat the area of a seed crystal which first comes into contact withsilicon melt is 5 mm² or less.

In the present invention, in the case of a seed crystal having atruncated shape of the tip end 4 c as shown in FIGS. 2(E) and 2(F), anangle of the tip end of the seed crystal refers to an apical angle ofthe tip end of the seed crystal when assuming a shape of the tip endbefore the tip end 4 c is truncated.

These seed crystals are used in manufacturing a single crystal so thateach of the straight bodies 3 c and 3 d of the seed crystals may belocked in a seed holder 28 of an apparatus 10 for manufacturing a singlecrystal shown in FIG. 1 via a locking part 2 c or 2 d provided on thestraight body 3 c or 3 d, respectively.

In the method of manufacturing a silicon single crystal according to thepresent invention, as shown in FIGS. 2(C), 2(D), 2(E) and 2(F), the tipends 4 c–4 f of the seed crystals have sharp-pointed shapes ortruncations thereof so that slip dislocations may not be introduced intothe seed crystals by thermal shock when the seed crystal comes intocontact with a silicon melt, or even if they are introduced, the amountthereof may be a little. They have obviously different shapes from seedcrystals used in Dash Necking method.

As examples of seed crystals utilized in growth of a silicon singlecrystal by means of Dash Necking method, FIG. 2(A) shows anapproximately columnar seed crystal and FIG. 2(B) shows a prismatic seedcrystal.

When growing a silicon single crystal, in order that a silicon singlecrystal to be grown may have a desired crystal orientation, the singlecrystal is grown by use of a seed crystal having the same crystalorientation as the single crystal to be grown. For example, in the caseof growing a single crystal having a crystal orientation of <110>, aseed crystal having a crystal orientation of <110> in the direction of apulling axis can be used.

When a seed crystal whose tip end has a sharp-pointed shape or atruncation thereof is dipped into a silicon melt, the seed crystal 1 cor 1 d shown in FIG. 2 is heated to approximately the same temperatureas the silicon melt M just above the melt. After the temperature of theseed crystal becomes steady, the tip end 4 c, 4 d or 4 e, 4 f is gentlydipped into the silicon melt M. When the tip end is dipped up to adesired diameter, then pulling is started. Thereby, a silicon singlecrystal S having an arbitrary decreasing diameter portion S0 shown inFIG. 1 is grown.

FIG. 1 is a schematic view showing an apparatus for manufacturing asilicon single crystal by a method of the present invention. Anapparatus 10 for manufacturing a single crystal is composed of a growingfurnace 12 where a silicon melt M is kept and growth of a single crystalis conducted, and an upper growing furnace 14 for storing and taking outa silicon single crystal S pulled from the silicon melt M.

At the top of the upper growing furnace 14, a winding and rotatingmechanism 26 for rotating and pulling the single crystal when growingthe crystal is installed. At the end of a wire 24 wound off from thewinding and rotating mechanism 26, a seed holder 28 for locking a seedcrystal 27 (the seed crystal 1 c or 1 d shown in FIG. 2 as an example)is located. When growing a single crystal, a straight body of the seedcrystal 27 is locked at the seed holder 28. The wire 24 is wound offfrom the winding and rotating mechanism 26, and a tip end of the seedcrystal is dipped into the silicon melt M up to a desired position, andthen the seed crystal 27 is pulled with being rotated at thepredetermined rate. Thereby, the silicon single crystal S is grown belowthe seed crystal 27.

Inside the growing furnace 12, a crucible 18 for containing the siliconmelt M is installed. Since it contains the silicon melt M having a hightemperature, the inside of the crucible 18 consists of a crucible madeof quartz 18 a, and the outside thereof consists of a crucible made ofgraphite 18 b for protecting the crucible made of quartz 18 a. Thecrucible 18 is disposed at the approximate center of the growing furnace12 by a crucible supporting shaft 16. Beneath the crucible supportingshaft 16, a crucible driving mechanism 20 is mounted in order to keep amelt surface constant when growing a single crystal, and in order togrow a crystal with rotating the crucible 18 in CZ method or MCZ method.

Furthermore, a heater made of graphite 23 for melting polycrystallinesilicon as a raw material and keeping it as the silicon melt M isdisposed outside the crucible 18, and an operation is performed whilekeeping a temperature of the silicon melt M at a temperature appropriatefor growth of a crystal by controlling the amount of heat from theheater 23.

Outside the heater 23 and at the bottom of the growing furnace 12, heatinsulators 22 and bottom heat insulators 21 are disposed, which keep theinside of the growing furnace 12 hot, and at the same time prevent awall of the growing furnace 12 from directly being exposed to radiationheat from the heater 23.

In the apparatus 10 for manufacturing a single crystal shown in FIG. 1,for the purpose of further stabilizing a temperature by controllingconvection of the silicon melt M, electromagnet 33, which is anapparatus for applying a horizontal magnetic field to the silicon meltM, is mounted outside the growing furnace 12.

In the apparatus 10 for manufacturing a single crystal, the center ofthe horizontal magnetic field is positioned inside the silicon melt M toefficiently suppress change in temperature of the melt, and thehorizontal magnetic field having intensity of 1000 G or more at thecenter of the magnetic field, which is a desired magnetic intensity, canbe obtained inside the silicon melt M when the seed crystal 27 isdipped.

From the beginning of growth of a single crystal to the time when atemperature of the inside of the furnace becomes a room temperature, itis necessary to perform the operation while flowing inert gas such asargon (Ar) inside the furnace in order to prevent the silicon melt M andstructural members disposed inside the apparatus 10 for manufacturing asingle crystal from being oxidized and so on. Therefore, a gas flowcontrolling device 30 for controlling a flow rate of the inert gasflowing inside the manufacturing apparatus 10 is installed in the uppergrowing furnace 14, and a pressure controlling device 32 for adjustingthe internal pressure is installed at the bottom of the growing furnace12. The flow rate of the inert gas flowing in the apparatus 10 ofmanufacturing a single crystal and the pressure thereof are adjusted byuse of these devices in accordance with growth conditions of a singlecrystal.

Next, the method of manufacturing a silicon single crystal according tothe present invention is explained in detail.

First, polycrystalline silicon as a raw material is charged into thecrucible 18, and the polycrystalline silicon is melted by heating fromthe heater 23. When all of the polycrystalline silicon is melted to be amelt, a temperature of the silicon melt M is decreased to thatappropriate for growth of a single crystal. At that time, whileadjusting conditions required for bringing the seed crystal 27 intocontact with the melt to be dipped, such as introduction of dopant andposition adjustment of a surface of the silicon melt M, application of amagnetic field starts so that the horizontal magnetic field with themagnetic field intensity of 1000 G or more at the center may be appliedto the silicon melt M by means of the electromagnet 33. This magneticfield is applied at least between the time when the tip end of the seedcrystal 27 comes into contact with the silicon melt M and the time whenformation of the decreasing diameter portion S0 formed below the seedcrystal 27 finishes and the enlargement of a diameter of the crystalstarts.

When the temperature of the silicon melt M reaches the predeterminedtemperature (preferably, a temperature 10–20° C. higher than atemperature appropriate to bring the seed crystal into contact with thesilicon melt in the method of manufacturing a silicon single crystalusing Dash Necking method), the seed crystal 27 having an apical angleof the tip end of 28° or less is lowered to directly above the siliconmelt M after the temperature becomes steady, and then stays until thetemperature of the tip end of the seed crystal 27 is heated toapproximately the same temperature as the silicon melt M.

Subsequently, when the seed crystal 27 is heated to approximately thesame temperature as the silicon melt M, and further a temperature of asurface of the silicon melt M around the center of the crucible 18 intowhich the seed crystal S is dipped is stabilized to the extent that thetemperature is changed in the range of ±5° C. or less, the seed crystal27 is gently brought into contact with the silicon melt M and dippedthereinto. In order to suppress the introduction of slip dislocations,it is preferable that the temperature variation of the surface at theportion of the silicon melt M where the seed crystal S is dipped is keptin the range of ±5° C. or less, preferably ±3° C. or less, at leastuntil the tip end of the seed crystal 27 is brought into contact withthe silicon melt M and then it shifts to pulling.

The descending rate of the seed crystal 27 is decreased to be stoppedwhen the tip end is immersed into the silicon melt M to thepredetermined diameter, and then it shifts to pulling while adjustingthe ascending rate of the seed crystal 27 and the temperature of thesilicon melt.

In shifting to pull the seed crystal 27, if the pulling rate is too fastor the temperature of the melt is not appropriate, occasionally the tipend of the seed crystal 27 detaches from the melt, or a diameter of acrystal formed at the tip end becomes smaller than the desired diameter.When shifting to pull the seed crystal 27, it is gently pulled whileobserving the diameter of the crystal formed at the tip end of the seedcrystal, and adjusting the pulling rate so that the diameter of thecrystal to be grown may not become smaller than the desired diameter.

In particular, immediately after shifting to pull the seed crystal 27,the crystal is formed while indicating a tendency that the diameter ofthe crystal to be grown at the bottom of the seed crystal 27 becomessmaller than the diameter of the tip end after immersion of the tip endof the seed crystal. If the diameter of the crystal is forcedly enlargedat that time, disadvantage may occur, for example, slip dislocations maybe introduced into the seed crystal 27, or the growing crystal may beseparated from the melt. Therefore, immediately after converting fromdipping into pulling, it is necessary to perform pulling with adjustingthe pulling rate so that the diameter of the crystal formed at the tipend of the seed crystal 27 may become slightly smaller than theimmersion diameter of the tip end portion of the dipped seed crystal 27(formation of the decreasing diameter portion S0). It is desirablypulled with keeping the pulling rate at this time at 0.5 mm/min or less.

As to the immersion diameter of the tip end of the seed crystal 27, itis necessary to perform dipping with considering that the crystal formedat the tip end when shifting to pulling once becomes thin.

After conforming formation of a crystal having a diameter smaller thanthe immersion diameter of the tip end at the bottom of the seed crystal27, the pulling rate and/or the temperature of the melt are graduallychanged to lead into an enlarging diameter process in which the diameterof the crystal is enlarged (formation of an enlarging diameter portionS1).

The diameter of the single crystal S formed below the seed crystal 27through the enlarging diameter process is enlarged to the desireddiameter, and the formation of the enlarging diameter portion S1 isstopped when it reaches the predetermined diameter. Then the pullingrate and/or the temperature of the melt are adjusted again to lead intoformation of a constant diameter portion S2 of the single crystal. Inthe formation of the constant diameter portion S2, the constant diameterportion S2 is pulled to be the predetermined length while adjustingoperation conditions in conformity to quality of the crystal to be grownand ambience inside the furnace (formation of the constant diameterportion S2).

Then, the growth conditions (a pulling rate, a temperature of a melt,etc.) is changed at the point when the formation of the constantdiameter portion S2 having the predetermined length has been completed,and the diameter of the crystal is gradually decreased to form a tailportion S3 (formation of the tail portion S3).

When the formation of the tail portion has been completed, the growncrystal is separate from the silicon melt M, and is wound up to theupper growing furnace 14. The silicon crystal S is taken out from theapparatus 10 for manufacturing a single crystal to its outside after thetemperature of the crystal lowers to a room temperature, and therebygrowth is finished.

If the single crystal grown in accordance with the above-mentionedmethod is subjected to cutting/cylindrical grinding process and then itis processed into a wafer having a mirror-surface by the well-knownmethod, a silicon wafer which is a main material for producing asemiconductor device can be obtained.

The present invention will be explained in detail hereinafter withshowing examples, but the present invention is not limited thereto.

(Experiment 1)

First, in order to study operation conditions desirable for growing asilicon single crystal having a crystal orientation of <110> which isdifficult to produce, a silicon single crystal having a diameter ofapproximately 150 mm (6 inches) in a constant diameter portion of thecrystal was manufactured using an apparatus for manufacturing a siliconsingle crystal shown in FIG. 1 and adopting a pulling method using DashNecking method without applying a magnetic field to a silicon melt.

As for a seed crystal, in order to grow a silicon single crystal whileeliminating dislocations by Dash Necking method, there was used a seedcrystal having a prismatic shape with sides of 15 mm and a crystalorientation of <110> (a seed crystal having a shape shown in FIG. 2( b))in which a surface for contacting with the silicon melt was flat.

A crucible made of quartz and having a bore diameter of 450 mm wasinstalled in an apparatus for manufacturing a silicon single crystal,and 60 kg of polycrystalline silicon as a raw material was filled intothe crucible. After gas inside the manufacturing apparatus was exchangedfor argon (Ar) gas, a heater made of carbon was heated to make thepolycrystalline silicon a silicon melt.

After confirming that all the raw material was melted, dopant wasintroduced so that a crystal to be grown might be p-type and might havea resistivity of about 10 Ωcm. Then the melt was left until thetemperature of the melt became steady, while the temperature of thesilicon melt was adjusted so as to lower to the temperature appropriateto growth of a single crystal. In the meantime, operation conditionssuch as the amount of inert gas (Ar gas) flowing in the manufacturingapparatus, pressure therein and rotation of the crucible were adjustedto the manufacturing conditions for growing a single crystal until thetemperature of the melt became steady.

Stability of the temperature of the melt was checked by measuring asurface temperature of the melt at the center of the crucible into whichthe seed crystal was dipped by use of a radiation thermometer(manufactured by CHINO, IR-02C), through a glass window provided toobserve the inside of the manufacturing apparatus from the outside ofthe apparatus for manufacturing a single crystal. When a temperatureappropriate to growth of a silicon crystal seemed to be obtained, thetemperature was measured.

A result was shown as “Range of temperature variation of melt” inTable 1. Although the surface temperature of the melt at the center ofthe crucible was repeatedly measured when the temperature seemed to besteady, the temperatures at the measured point repeatedly changed up anddown within a range of ±6° C., and the range of the temperaturevariation never became smaller.

The measurement of the temperature was stopped at that time. After theseed crystal was heated at just above the silicon melt for about 5minutes, it was gently brought into contact with the silicon melt andmelted, and elimination of slip dislocations was tried using DashNecking method.

However, it was difficult to eliminate slip dislocations in the seedcrystal having a crystal orientation of <110> by Dash Necking method.After elimination of dislocations failed five times, slip dislocationswere eliminated when the minimum diameter of a neck portion of thecrystal was decreased to 2 mm in the sixth Dash Necking, and thus makingdislocation free at the neck portion succeeded.

Although elimination of dislocations at the neck portion by Dash Neckingmethod succeeded, since the temperature variation of the silicon meltmight be large, slip dislocations were introduced into the singlecrystal when the constant diameter portion of the crystal was grown to60 cm. Consequently it was impossible to pull the crystal withoutdislocations. (See column “Presence or absence of success in pulling acrystal” in Table 1. O mark indicates a case where a silicon singlecrystal without dislocations was pulled, and X mark indicates a casewhere a silicon single crystal without dislocations could not be grown.)

As to results of Experiment 1 and after-mentioned Experiment 2 andExample 1, details are shown in Table 1 for comparison.

TABLE 1 (Results of growing a silicon single crystal having a crystalorientation of <110>) Intensity of applied The magnetic number Presencefield of Range of or absence (horizontal Diameter failure temperature ofsuccess magnetic of grown Method for in variation of in pulling field)crystal necking seeding melt a crystal Experiment 1 Not applied 15 cmDash Necking 6 times   ±6° C. X method Experiment 2 Not applied 20 cmDislocation- 9 times   ±8° C. X free seeding method Example 1 4000 G 20cm Dislocation- 0 time ±1.5° C. ◯ free seeding method(Experiment 2)

From Experiment 1, it was found that there was a limit to elimination ofslip dislocations by Dash Necking method as a method for pulling a heavycrystal with a large diameter since a success ratio was low in the caseof a single crystal having a crystal orientation of <110> and inaddition, there was a need to thin the minimum diameter of the neckportion up to about 2 mm in order to eliminate dislocations.

A single crystal having a diameter of about 200 mm (8 inches) at aconstant diameter portion was practically pulled in order to confirmwhether a single crystal having a large diameter could be grown by amethod for growing a dislocation-free silicon single crystal using aseed crystal having a sharp-pointed tip end without using Dash Neckingmethod (hereinafter, referred to as dislocation-free seeding method).

Using the same apparatus as Experiment 1 as an apparatus for growing asingle crystal, manufacture was conducted without applying a magneticfield to a silicon melt. In Experiment 2, in order to grow a siliconsingle crystal having a diameter of about 200 mm and a crystalorientation of <110>, a crucible made of quartz and having a borediameter of 600 mm was installed in the manufacturing apparatus, and 150kg of polycrystalline silicon as a raw material was charged and became asilicon melt through heating as in Experiment 1.

By the time that the temperature of the silicon melt was stabilized at atemperature appropriate to growth of a single crystal, dopant wasintroduced into the melt so that resistivity of a p-type crystal mightbe a value of about 10 Ωcm. Then operation conditions such as Ar gasflow and pressure inside the manufacturing apparatus were adjusted, andit was left until the temperature became steady.

As to a seed crystal used in Experiment 2, since there was a need toperform pulling while avoiding introduction of slip dislocations due tothermal shock without using Dash Necking, a seed crystal having a shapeshown in FIG. 2(C), which had a columnar straight body with a diameterof 15 mm and a sharp conical tip end with an apical angle of 15°, wasused.

When the temperature of the silicon melt was stabilized at thetemperature of 13° C. higher than the temperature at which the seedcrystal was brought contact with the silicon melt in Experiment 1, asurface temperature of the silicon melt at the center of the cruciblewas measured by using the radiation thermometer as in Experiment 1 fromthe outside of the manufacturing apparatus. As a result, it wasrepeatedly changed up and down within a range of about ±8° C. as shownin Table 1. However, it was impossible to make the range of temperaturevariation small any more and to adjust the temperature of the melt to besteady.

In this condition, the seed crystal was gently lowered to 1 mm directlyabove a surface of the silicon melt and heated for about 20 minutes tillthe temperature of the seed crystal became approximately the same as thetemperature of the melt. Thereafter the seed crystal was brought intocontact with the silicon melt and immersed into the melt to the desireddiameter, and then the seed crystal was gradually pulled while keepingthe pulling rate at 0.5 mm/min or less. Thereby formation of a siliconsingle crystal below the seed crystal was tried.

However, in most cases, slip dislocations possibly due to thermal shockwere introduced into the seed crystal while the tip end of the seedcrystal was dipped into the melt to the desired diameter. Althoughtrying to grow crystals using the same dislocation-free seeding methodfor 9 times while changing the seed crystal in each time, it wasimpossible to pull a dislocation-free single crystal in all the 9 times.

As the reason thereof, it is considered that since the crucible becamelarger to increase the amount of silicon melt contained therein,temperature difference of the silicon melt in the crucible was enlargedand the temperature of the melt was destabilized, and therefore slipdislocations were introduced into the seed crystal in process ofdipping.

From the result of Experiment 2, it was found that, in order to grow asilicon single crystal while preventing introduction of slipdislocations due to thermal shock by use of a seed crystal with asharp-pointed tip end and without using Dash Necking method, there was aneed to further suppress the temperature variation of the silicon meltwhen dipping the seed crystal.

(Experiments 3–5)

Influence of a temperature variation of a silicon melt when dipping aseed crystal on slip dislocations in the seed crystal was studied. As amethod for controlling the temperature, certain growth conditions asshown in Table 2 regarding Experiments were set, and in Experiment 3 amagnetic field having intensity of 500 G was applied, in Experiment 4 amagnetic field having intensity of 750 G was applied, and in Experiment5 infrared was irradiated by means of lamp heating to a surface of thesilicon melt in order to suppress natural convection due to thermalexpansion by decreasing the difference of temperature in the depthdirection of the silicon melt and thereby to lower the temperaturevariation. As to presence or absence of slip dislocations in the seedcrystal, the diameter was enlarged to 200 mm after the seed crystal wasdipped to the predetermined length and subsequently a decreasingdiameter portion was formed, and then judgment on nonexistence ofdislocations was conducted by checking crystal habit lines indicating acondition of a single crystal. This is a general method in whichcrystallization of a single crystal can be easily judged since acharacteristic crystal habit to be generated on a surface of a singlecrystal disappears in the case that dislocations remain in the seedcrystal. As a seed crystal, a seed crystal having a shape shown in FIG.2( c) was used, which had a columnar straight body with a diameter of 15mm and a sharp conical tip end with an apical angle of 15°.

TABLE 2 (Results of dislocation generation in a silicon seed crystalhaving a crystal orientation of <110>) Intensity of applied Range ofmagnetic field Bore of temperature State of (horizontal quartz Theamount variation of dislocation magnetic field) crucible of silicon meltmelt generation Experiment 3 500 G 600 mm 150 kg  ±10° C. Presence ofdislocations Experiment 4 750 G 600 mm 150 kg ±5.6° C. Presence ofdislocations Experiment 5  0 G 600 mm 150 kg ±4.3° C. Absence ofdislocation

From Experiment 4 and Experiment 5 in Table 2, it was found that thecrystal habit lines on the surface of the crystal disappeared at anenlarging diameter portion and dislocations were generated under theconditions that the range of the temperature variation of the meltexceeded 5° C. Further, from Experiment 5, it could be confirmed that itwas possible to grow a single crystal without generating dislocations ifthe range of the temperature variation of the melt was 5° C. or less.

In the case of controlling the temperature variation of the silicon meltby applying a magnetic field in growth conditions as Experiment 2, if amagnetic field of 1000 G or more was applied, the range could becontrolled within ±5° C. It is found that application of a magneticfield with such a level is effective, although the optimal intensity ofa magnetic field and so forth are slightly different depending on thegrowth conditions and so forth. In the present invention, it isimportant to control the temperature variation of the silicon melt,particularly, to control it within ±5° C. Therefore, when it could becontrolled in such a condition, methods except for a method of applyinga magnetic field were also effective.

EXAMPLE 1

In order to grow the same single crystal having a diameter of about 200mm and a crystal orientation of <110> as Experiment 2, growth of asilicon single crystal was tried, in which a seed crystal was broughtinto contact with a silicon melt and dipped therein while applying ahorizontal magnetic field to the silicon melt.

The same apparatus as used in Experiment 2 was utilized, and a cruciblemade of quartz having a bore diameter of 600 mm was installed in theapparatus. 150 kg of polycrystalline silicon was charged therein and theraw material was heated by a heater made of graphite to become a siliconmelt.

When all the polycrystalline silicon was melted, the temperature thereofwas decreased to the desired temperature suitable for growth of a singlecrystal. Then dopant was added into the melt so that resistivity of ap-type crystal might be 10 Ωcm, and it was left until the temperature ofthe melt became steady. In the meanwhile, an apparatus for applying amagnetic field (electromagnet) which was located outside the apparatusfor manufacturing a silicon single crystal was operated, and ahorizontal magnetic field having intensity of 4000 G at the center ofthe magnetic field was applied to the silicon melt.

In Example 1, application of the magnetic field was continued from thetime when the melting was finished and stabilization of the temperatureof the melt was set out until the time when the growth of the siliconsingle crystal was finished and a tail portion of the crystal wasseparated from the melt.

After applying the magnetic field to the silicon melt, a surfacetemperature of the melt around the center of the crucible was measuredby the radiation thermometer as Experiment 2 when the temperature of themelt seemed to be stabilized at approximately the same as thetemperature in Experiment 2. The temperature variation was settledwithin ±1.5° C., and therefore it was confirmed that it was kept in goodcondition for bringing a seed crystal into contact with the melt.

A seed crystal having the same shape as Experiment 2, which had adiameter of 15 mm in the straight body, a sharp conical tip end with anapical angle of 15°, and a crystal orientation of <110>, was loaded in aseed holder of the manufacturing apparatus.

After confirming stabilization of the temperature of the melt, the seedcrystal was gently lowered to 1 mm directly above the silicon melt, andit was left for about 20 minutes until the seed crystal was heated. Thenafter the seed crystal was heated to the temperature as much as thetemperature of the silicon melt, the tip end of the seed crystal wasgradually lowered into the melt and the conical portion of the tip endof the seed crystal (the tip end portion) was immersed into the siliconmelt up to a desired diameter.

When the seed crystal was immersed to the desired diameter, lowering ofthe seed crystal was stopped and pulling started gently. When thetemperature variation of the surface of the silicon melt between thetime of bringing the seed crystal into contact with the silicon melt andthe time of shifting to the pulling was measured by means of theradiation thermometer, it was confirmed that the temperature variationwas kept within a range of ±1.5° C. Then, a decreasing diameter portionwas formed below the seed crystal while keeping the pulling rate of theseed crystal at 0.5 mm/min or less and controlling the temperature ofthe silicon melt, and after that, the diameter of the crystal wasenlarged to the predetermined diameter to grow a silicon crystal havinga diameter of about 200 mm in the constant diameter portion.

After growing the constant diameter portion so that the constantdiameter portion of the single crystal might have the predeterminedlength, the diameter of the crystal was gradually lessened to form atail portion and the grown crystal was separated from the silicon melt.Thereby the growth of the silicon single crystal had been finished.

The grown silicon single crystal was gently cooled, and it was taken outof the manufacturing apparatus. When its weight was measured, a heavysingle crystal with a large diameter shown in FIG. 3 was obtained, whichhad a diameter of 208 mm and weight of 120 kg. Further, there was nofailure such that a crystal was grown again from the beginning due tointroduction of slip dislocations during growth, and therefore it waspossible to grow a heavy single crystal with a large diameter which wasdislocation-free and had an intended crystal orientation of <110>without any difficulty. Moreover, as a result of the measurement afterthe pulling, it was confirmed that the minimum diameter of thedecreasing diameter portion formed at the tip end of the seed crystalshown in FIG. 3 was 5 mm or more, and therefore a single crystal couldbe grown without using Dash Necking method.

Thereby, according to the manufacturing method of the present invention,it was found that it was possible to optimally manufacture even asilicon single crystal with a crystal orientation of <110>, which hadbeen thought impossible to be grown as a heavy single crystal with alarge diameter, by CZ method including MCZ method.

Further according to the present invention, it was found that, in thecase of adopting the dislocation-free seeding method in which a siliconsingle crystal was grown by using a seed crystal having a tip end with asharp-pointed shape or a truncation thereof without using Dash Neckingmethod, the ratio of success could be improved.

The present invention is not limited to the embodiments described above.The above-described aspects are mere examples, and those havingsubstantially the same structure as technical ideas described in theappended claims and providing the similar functions and advantages areincluded in the scope of the present invention.

For example, the embodiments of the present invention were explainedwith referring to an example of growing a silicon single crystal havinga diameter of 200 mm (8 inches), however, the effects of the presentinvention can be sufficiently obtained also in the case of growing asilicon single crystal having a smaller diameter. Further the presentinvention is also effective in increasing the weight since there is noneed to perform necking of a seed crystal by Dash Necking method. Forexample, in the present invention, since the diameter of 5 mm or morecan be ensured even at the minimum diameter portion of a crystal formedat the tip end of a seed crystal, the present invention can be alsoapplied to manufacture of a silicon single crystal with a large diameterof 300 mm (12 inches) or more which have been widely utilized in recentyears, particularly, a heavy silicon single crystal having weight of thecrystal over 300 kg.

In the embodiments, examples of a crystal orientation of <110> which ismost difficult in pulling were explained, however, the present inventioncan be also properly applied to pulling of crystals having other crystalorientations. Pulling a crystal having a crystal orientation of <100> or<111> is not difficult compared with pulling a crystal of <110>, but themethod according to the present invention is still effective sincefrequency of failure of seeding decreases.

1. A method of manufacturing a silicon single crystal by Czochralski method without performing Dash Necking method, comprising: providing a seed crystal having a tip end with a sharp-pointed shape or a truncation thereof in which an angle of the tip end is 28° or less; keeping the tip end of the seed crystal at just above a silicon melt to heat it before bringing the tip end of the seed crystal into contact with the silicon melt; subsequently, bringing the tip end of the seed crystal into contact with the silicon melt and immersing the seed crystal into the silicon melt to a desired diameter; and then shifting to pull the single crystal, wherein a temperature variation at a surface of the silicon melt is kept at ±5° C. or less at least for a period from a point of bringing the tip end of the seed crystal into contact with the silicon melt to a point of shifting to pull the single crystal, wherein the seed crystal is brought into contact with the silicon melt and immersed therein with setting a temperature of the silicon melt when bringing the tip end of the seed crystal into contact with the silicon melt to 10–20° C. higher compared to a temperature used for bringing the seed crystal into contact with the silicon melt in a method of manufacturing a silicon single crystal in Dash Necking method, and wherein the single crystal is pulled with setting a pulling rate to 0.5 mm/min. or less when forming a decreasing diameter portion for a period from a point immediately after stopping lowering of the seed crystal and shifting to pulling to a point of starting enlargement of a diameter of the crystal formed below the seed crystal.
 2. The method of manufacturing a silicon single crystal according to claim 1, wherein the single crystal is pulled while a horizontal magnetic field with a magnetic field intensity of 1000 G or more at a center thereof is applied to the silicon melt at least for a period from a point of bringing the tip end of the seed crystal into contact with the silicon melt to a point of completing formation of a decreasing diameter portion formed below the seed crystal and starting enlargement of the diameter of the crystal.
 3. The method of manufacturing a silicon single crystal according to claim 1, wherein a silicon single crystal having a crystal orientation of <110> is pulled by using a seed crystal having a crystal orientation of <110>.
 4. The method of manufacturing a silicon single crystal according to claim 2, wherein a silicon single crystal having a crystal orientation of <110> is pulled by using a seed crystal having a crystal orientation of <110>. 